Magnetometers



May 27, 1958 c. H. KAPLAN 2,836,791

fric-2 2.

May 27, 1958 c. H. KAPLAN 2,835,791

MAGNETOMETERS Filed July 29, 1953 4 sheets-sheet 2 C. H. KAPLAN May 27, 1958 MAGNETOMETERS 4 Sheets-Sheet .'5

Filed July 29, 1953 l af C. H. KAPLAN May 27, 1958 MAGNETOMETERS 4 Sheets-Sheet 4 United Sjtates atent O MAGNEToMErERS Charles Heiman Kaplan, Montrouge, France, assignor to Compagnie pour la Fabrication des Compteurs et Materiel dUsines Gaz, Montrouge, Seine, France, a joint-stock company of France Application July 29, 1953, seria! No. 37e,96s `Claims priority, applicatieii France July 31, 1952 6 Claims. (ci. 324-43) The present invention is concerned with magnetometers of the kind which are used for the determination by one single measurement of any particular component oi'a magnetic field.

Such magnetometers are known, of the type which contain an element sensitive to the magnetic eld, and in which a magnetic eld of opposite sign is created by a current passing through a solenoid which surrounds the said sensitive element, the intensity of the field being determinated by the value of the current necessary to return to the zero point of its graduation, the galvanometer interposed in the circuit of the element which is sensitive to the magnetic field.

A magnetometer of this type is shown diagrammatically in Fig. l. 1 of alternating current which supplies the primary winding of a transformer 2. 3a and 3b represent two identical solenoids, within the interior of which are respectively located the cores 9a and 9b which are made of a ferro-magnetic alloy of high primary permeability. One end of each of these solenoids is connected to one extreme terminal of the secondary of the transformer 2, whilst the two other extremities are joined together at the point 10. Between the centre-point tapping 11 of the secondary winding of the transformer 2 and the common point of the two ends of the solenoids 3a and 3b, there is connected a continuous-current galvanometer 4, across the terminals of which there is connected a condenser 5. Around the two solenoids 3a, 3b, there is wound a third solenoid 6, which will be termed hereafter the compensating solenoid, and which is connected in a circuit which'includes a source of continuous current 7, a controlling rheostat 8, a change-over switch 12 and a milliammeter 13.

When there is no magnetic field acting on the cores 9a and 9b, the latter saturate themselves symmetrically in function of time, the magnetisation curves of each of these cores being displaced by 180 so that no current passes through the branch 10-11. If an external magnetic field acts on the cores 9a and 9b, the component of this eld which follows the magnetic axis of these cores produces a dissymmetry in the magnetisation of the cores 9a and 9b. This dissymmetry causes a distortion of the current curves corresponding to the appearance of even harmonics in the magnetising current. By means of, for example, two non-linear resistances 24 which can be placed in series with each of the windings 3a, 3b, there is obtained in the circuit of the galvanometer 4, a rectified current, the alternating component of which is eliminated by the condenser 5. The operator causes a current to pass through the solenoid 6, the direction and the value of Vthis current being such that the needle of the galvanometer 4 is brought back to the` zero point of its scale. The current passing through the solenoid 6, which is necessary to reduce the current in the branch 10-11 to zero, is measured by the milliammeter 13. This current is proportional tothe compo- There is shown in this figure a generator nent of, the field which follows the magnetic axis ofV theV v K Zgl Patented May 27, 1%58 cores 9a and 9b. The apparatus 13 may be graduated in gauss (or in sub-multiples of gauss) so that the deection of the needle will give a direct indication of the component of the eld along the magnetic axis of the cores 9a and 9b.

This magnetometer has the drawback of requiring the intervention of an operator to regulate the current in the circuit of the solenoid 6 every time there is a variation in the magnetic field detected.

The object of the present invention is to overcome this drawback. The invention is characterised by means whereby the control of the current in the compensating solenoid is automatically eiected by the out-of-balance current due to the magnetic dissymmetry in at least one ot the cores made of an alloy of high primary permeability.

To this end, the invention contemplates the replacement of the galvanometer 4 by any automatic compensating device of known kind, such as a measurement converter, an automatic potentiometer, either electrical or non-electrical, electronic or other amplifier, etc.

In the examples shown, the automatic compensating device is a measurement converter, the moving frame of which, with the opposing couple removed of the galvanometer inserted in the circuit of the element which is sensitive to the magnetic field, is rigidly coupled to the variable member of a device by means of which there s obtained a direct current passing through the solenoid 6, the direction and the value of this current controlling itself automatically so as to obtain a compensation of the variations of the magnetic field in the sensitive elements of the magnetometer.

The solenoid 6 may comprise several sections thus permitting the calibration of the magnetometer to be varied.

In acordance with an alternative embodiment of the invention, the element sensitive to the magnetic field is surrounded, in addition to the solenoid 6, by a second solenoid which is connected to the terminals of a source of direct current, the strength of which is variable, either by the operator or by an automatic device, by means of which, in the irst place, the earths magnetic eld may be compensated, or the magnetic field, the variations ot which are ultimately desired to be indicated.

In accordance with another form of embodiment of the invention, the circuit containing the source of direct current is connected in parallel across the terminals of the solenoid 6, so that the total current which passes through this solenoid compensates at the same time for the earths magnetic eld (or the magnetic eld, the variations of which it is desired to indicate) and the variations of these magnetic fields.

The above mentioned alternative embodiment may comprise the following modifications: A circuit with a universal shunt connected in parallel across the terminals oi the solenoid 6, is inserted in the automatic compensation device so that the current which leaves this device is divided between the shunt and the solenoid.

In accordance with still a further modification, the compensating solenoid only surrounds one of the two cores of ferro-magnetic alloy with a high primary permeability.

The invention is also concerned with certain methods of application of the said arrangements, in particular the application to the measurement of direct current of high intensity based on the action of the magnetic field created by the bar through which such a current passes.

Figs. 2, 3, 4, 5 and 6 of the accompanying drawings show, by way lof example only and not in any way `by limitation, different forms of embodiment of the invention.

Fig. 7 shows the device in accordance with the inven- Vample shown, is a condenser.

tion when it is applied tothe measurement ot direct curt rent of high intensity.

Fig. 8 is'an alternative form of Fig. 7 in which the element which is sensitive to the magnetic field is constituted by two magnetic circuits which surround the bar carrying the directV current of high current value.

asse-,7.9i

ln Fig. 2, in VwhichV theV reference numbersv 1 Y2 l3o, 'i

3b, 5, 6, '112,711 and i3 have the same meaning as in nection 22 a high-frequency voltage, while the other, 19.,"

is connected to one end of anV impedance 21, theother extremity ofwhich is connected to earth at 22. There is thus obtained across the terminals of the impedance 21, a difference of potential which is a function of the position of the moving plates 17 and, in consequence, is alsov a function of the position of the moving coilV 14..- The potential across the terminals of the impedance 21 is applied to the input terminal of an amplifier-detector 23 of any known type.

The direct current voltage developed across the output terminals ofrthisamplier-detector is applied to a kcircuit the milliammeter- 13 which` includes the solenoid 6 and which issraduated in sauss.

When the detected magnetic ield varies, the moving Y coilf rotates either in one direction or the other,=and Y thereby causes the capacity of the condenser 16 to vary by. virtue of the location of the set of plates V17 which are, rigidly'cDT-lpled to the moving coil 14. This results in a variationV of current owing through the impedance 21 and, in consequence',Y a variation Aof potential across the 'output terminals'of the ampliendetector 23. This Vvariation ofppotentialv induces a variation of current in the solenoid 6,V the direction and the VVvalue of which are such Athat the magnetic uX produced by this solenoid compensates exactly forV the variation of the component ofthe detected magnetic field. There is thus obtained an automatic control of theV current which is used for the measurement of the saidV magnetic field.V

In the alternative embodiment Vin accordance with Fig. 3, the. arrangement shown isV the same as that of Fig. 2, but the solenoids 3a, 3b vare surrounded, in addi-V tion, by a second solenoid 6 connected in a circuit which comprises a source' of direct current`V 31, a rheostat 32, achange-over switch 53 and aV milliarnmeter 34.

Y current flowing in the circuit ofthe solenoid 6' is varied by the operatorwho controls the rheostat 32 injsuch aV way Vthat the pointer of the milliarnmeterA i3 is restored to the zero point of its graduation. in these conditions, the pointer of the milliammeter i3 will onlyfshowva de ection if the magneticneid'- detected varies. VThis arrangement enables the sensitivity of the magnetometer'to Y Vbe increased to a very high degree.

The valueA of the total magnetic lieldis obtained at anyrequired to be detected (the circuitrincluding the source 31 of direct current, the rheostat 32, thechange-over switch 33 and the milliammeter 34), is connected in shunt across the terminals Vof the solenoid 6. This arrangement enables the second solenoid, indicated at 6' in Fig. 3, to be dispensed with.

Fig. shows a modication ofthe form of embodimentl given in Fig.'4. A universal shunt 101 with multipleV tappingrsand a fixedv resistance 102; are lconnected in parallel across the terminals ofthe, solenoid 6. The universal shunt 101 is furthermore'inserted Vin the output circuit of the amplifier-detector 23 in series with the milliammeter 13.

In the alternative embodiment shown inVV Fig. solenoid 6 which is provided Ifor the automaticcompensation, only Surrounds the magnetic core 9a. The solenoid Y 6 comprises two windings 6a andfti'b.Y By'this'means,

the. twosensitive elmentsmay bie .separated and theymay be located ata considerabledistance from each other. Y

The two Ysensitive elements are-iirstV ot? all. placed inV theV same magnetic eld and the current in the windings aj and 'bis regulated in such a wayas to bringthe, pointer of the milliamrneter 13 back to zero.

The magnetometer being thus calibrated,'the sensitive element comprising `the core Salis moved to a-certain distance;V lf the magnetic, field; is thesame as it was before, the,V milliammeter 13 remains a't zero, but ifY the contrary is the case, it. shows a deflection which gives a direct indication of the difference between the two fields. Y

Although several forms of embodiment of the invention have been shown, it is quite clearvthat the invention is not to; belimited to those particular forms, which have been: given simply by way of examplegand which-have no restrictive nature, and-that in consequence, Vall the alternative forms of embodiment havingl the same principle and the same object as the arrangement referred to above,

would, like those arrangements, fall withinthe scope of the present invention.

lnrparticulanthe variable element associated with the moving coil ofrthe galvanometer, having its countercouple removed (which element Vinfth'ey case of theV ex. t

amples shown in the moving plates of a condenser) may be themoving coil of a mutual inductance coil placedA inY the magnetic ield produced by the lixed winding which is -supplied from an alternating current source. This variable element may alsoV bea mirror which Vdirectsa lumi nous beam on to a photo-electric cell or again it may be a bolometer device.

instant by adding togethery the indications of theV two milliammeters 34 and 13. p

VIn the alternative embodiment shownA in Fig. 4, the arrangement shown. is based on the same principle as that ofrFig. 3, but the circuit which is provided Vto compensate for the component of V'the earths magnetic-field: or ofthe magnetic field, the variationsV or" which are Fig. 7 shows a diagrammatic form of the arrangement of Fig. 2 applied to the measurement of a direct curren kof high intensity flowing through abar.

In this grure, where the various circuit have the same reference'numbe'rs as in Fig.r 2, `B repre-V sents a bar through which passes a direct'current I of,V

high intensity. ThisV direct current produces, als is well known, a magnetic field H, the lines of force, of'which are circles, the axis of' which isv the bar B. vThe value of this magnetic eld is proportionalA to the direct current I which passes throughV 'the bar B andfis inversely proportional to the distancegbetween the centre of the bar and the element which isY sensitive to the magneticV field. The determination of the magnetic ield produced by the current I which passes through the bar B thus Yenables Vthe intensity of the said' current to Ibe readily 1. A magnetometer comprising. acircuit sensitive ftoa 'magnetic field constituted by two identical solenoids arranged in parallel, each.V containing a coreof highinitial permeability; 'thecircuitl which vincludes them being sup-v 67, the

components En o plied from a source of alternating current, the amplitude of which produces saturation of the said cores, the said source of alternating current comprising a generator and a transformer, one of the ends of each of the two solenoids being respectively connected to one of the extreme terminals of the secondary winding of the transformer, the two other extremities being joined together and connected to the centre point of the said secondary winding, a galvanometer the moving coil of which without countercouple is included in the connection which joins the centre point of the secondary of the transformer to the common point of the extremities of the two solenoids, and a compensating arrangement constituted by a compensating solenoid surrounding the two solenoids of the circuit which is sensitive to the magnetic field, an oscillator generating a potential at high frequency, a variable member, the moving part of which is rigidly associated with the moving coil of the galvanometer, an impedance, an amplifier-detector, the input terminals of which are connected to the terminals of the said impedance and the output terminals of which supply the said compensating solenoid and an apparatus which measures the output current.

2. A magnetometer comprising a circuit sensitive to a magnetic iield constituted by two identical solenoids arranged in parallel, each containing a core of high initial permeability, the circuit which includes them being supplied lfrom a source of alternating current, the amplitude of which produces saturation ofthe said cores, the said source of alternating current comprising a generator and a transformer, one of the ends of each of the two solenoids being respectively' connected to one of the extreme terminals of the secondary winding of the transformer, the two other extremities being joined together and connected to the centre point of the said secondary winding, a galvanometer the moving coil of which without countercouple is included in the connection which joins the centre point of the secondary of the transformer to the common point of the extremities of the two solenoids, and a compensating arrangement constituted by a compensating solenoid surrounding the two solenoids of the element which is sensitive to the magnetic field, an oscillator generating a potential at high frequency, a variable member, the moving part of which is rigidly associated with the moving coil of the galvanometer, an impedance, an amplifier-detector, the input terminals of which are connected to the terminals of the said impedance and the output terminals of which supply the said compensating solenoid and an apparatus which measures the output current, a variable condenser which has a set of moving plates associated with a spindle of the moving coil of the galvanometer and two sets of fixed plates, one con-V nected to the oscillator, the other connected to one of the terminals of the said impedance.

3. A magnetometer comprising a circuit sensitive to a magnetic eld constituted by two identical solenoids arranged in parallel, each containing a core of high initial permeability, the circuit which includes them being supplied from a source of alternating current, the amplitude of which produces saturation of the said cores, the said source of alternating current comprising a generator and a transformer, one of the ends of each of the two solenoids being respectively connected to one of the extreme terminals of the secondary winding of the transformer, the two other extremities being joined together and connected to the centre point of the said secondary winding, a galvanometer the moving coil of which without countercouple is included in the connection which joins the centre point of the secondary of the transformer to the common point of the extremities of the two solenoids, a compensating arrangement constituted by a first compensating solenoid sturounding the two solenoids of the element which is sensitive to the magnetic field, an oscillator generating a potential at high frequency, a variable e. member, the moving'partof which is rigidly associated with the moving coil of the galvanometer, an impedance, an amplifier-detector, the input terminals of which supply the said compensating solenoid and an apparatus which measures the output current, and a second compensating solenoid also surrounding the two solenoids of the circuit which is sensitive to the magnetic eld, a source of direct current, a rheostat, a change-over switch and a milliammeter, the said second solenoid Ibeing in circuit with the said source of current as are also the changeover switch and the milliammeter, the value of the current in this latter circuit, measured by this latter milliammeter, being regulated in such a way that the magnetic ux of the second compensating solenoid in the circuit which is sensitive to the magnetic field compensates for the component of a constant magnetic tield, the rnilliammeter connected in the circuit of the rst compensating solenoid, giving indications which are proportional only to the variations of the magnetic field to be measured.

4. A magnetometer comprising a circuit sensitive to a magnetic eld constituted by two identical solenoids arranged in parallel, each containing a core of high initial permeability, the circuit which includes them being supplied from a source of alternating current, the amplitude of which produces saturation of the said cores, the said source of alternating current comprising a generator and a transformer, one of the ends of each of the two solenoids being respectively connected to one of the extreme terminals of the secondary winding of the transformer, the two other extremities being joined together and connected to the centre point of the said secondary winding, a galvanometer the moving coil of which without countercouple is included in the connection which joins the centre point of the secondary of the transformer to the common point of the extremities of the two solenoids, a compensating arrangement constituted by a compensating solenoid surrounding the two solenoids of the element which is sensitive to the magnetic iield, an oscillator Y generatinga potential at high frequency, a variable member, the moving part of which is rigidly associated with the moving coil of the galvanometer, an impedance, an amplier-detector, the input terminals of which are connected to the terminals of the said impedance and the output terminals of which supply the said compensating p solenoid and an apparatus which measures the output current, and by a second circuit including a source of direct current, a rheostat, a change-over switch and a milliammeter, this circuit being connected in parallel across the terminals of the compensating solenoid, the value of the current which passes through the said circuit and the said compensating solenoid, measured on the latter milliammeter, being adjusted in such a way that the magnetic flux of the said compensating solenoid in the circuit which is sensitive to the magnetic eld compensates for the component of a constant magnetic eld, the milliamrneter connected in the circuit of the compensating solenoid giving indications which are proportional only to the variations of the magnetic field to be measured,

5. A magnetometer comprising a circuit sensitive to the magnetic field constituted by two identical solenoids arranged in parallel, each containing a core of high initial permeability, the circuit which includes them being supplied from a source of alternating current, the amplitude of which produces saturation of the said cores, the said source of alternating current comprising a generator and a transformer, one of the ends of each of the two solenoids, being respectively connected to one of the extreme terminals of the secondary winding of the transformer, the two other extremities being joined together and connected to the centre point of the said secondary winding, a galvanometer the moving coil of which without countercouple is included in the connection which joins the centre point of the secondary of the transformer to the common point of the extremities of the two solenoids, a

compensatingarrangementconstituted by la compensating A' solenoid surrounding the rtwosolenoids of the element which is sensitive to the magnetic field, an oscillator generatirigV a potential at high frequency, a variable member, the moving part of which is rigidly `associated with the movingcoiliot"Y the galvanometer, an impedance, an amplifier-detector, the/input terminals of which are connected a way that themagnetic flux vof the said compensating.

solenoidtin the circuit which is sensitive to the magnetic field, compensates for the component of a constant magnetic field, the milliammeter connected in the circuit of the compensating solenoid giving indications which are-proportional only. to the Ivariations of the magnetic field which is to bermeasured.

6. A'magnetometer comprising a circuit sensitive to the magnetic field constituted :by two identical solenoids arrangedin parallel, each containing a core of high initial permeability, thecircuit which includes them being supplied from a source of `alternating current, the amplitude of which produces saturation of the said cores, the said source of alternating current comprising a generator and a transformer, one of the ends of each of the `two solenoids being respectively connected to one of the extreme terminals ofthe secondary winding of the transformer,

Y is a galvanometer the moving coil of which without countercouple is included in the connection which joins the I tield, an osci-llator generating a .potential-athigh frequency, a variable member, the moving part of Whichis rigidly centre* point of the 'second-ary lofthe transformer tothe L common point of the extremities ofthe two-solenoids, and a compensating lanizmgement constituted by a first;

compensating solenoidjsurroundingone ofthe two solenoids of the element whichris sensitive tothe magnetic associated with thejmov'ingcoil of the galvanometenan impedance, an amplifier-detectoiythe input terminals of which are connected to the terminals of the said impedance and output terminals ofY whichV supply the said compensating solenoid and an apparat-us which measuresV thefoutput current, arid two other compensating solenoids, each surrounding-oneofl the two solenoids ofthe circuit which is sensitive to the magnetic field, a source of 'direct current. a rheostat, a change-over' switch anda milliam-V t meter, these two latter solenoids being incircuit with the;

said source ofv current. aswell as the change-over switch andthe milliammeter, the value of the currentl owing in this, latterrcircuit, measured: by this latter milliammeter, f being` adjusted in suchk manner, that the magnetic flux of the two latter solenoidsfinl the circuit which is sensitive to the magnetic field compensates-for the componentof a constant magnetic field, the milliammeter'connected in Ythe circuitof the first compensating solenoid-,giving indications which are proportional only` to the variations'ofg the componentolf*thcmagneticfield whichV is to be meas- '1 ured. Y

References. C itfed in the file of this patent t UNITEDASTATES PATENTS aerea??V Thomas \oct.'s,19'35 2,406,870 Vacquier Sept.l3, 19,46" 2,421,583 Stuart .lune 3,1947Y 2,584,571` Frowe Feb. 5, 1952V 2,605,302-

y Specht 'July 29,1952'l 

